Calorimetric evaluations of Bacillus subtilis vegetative and spore cells colonial growth and suppressive effects of sucrose monopalmitate.

The colonial growth of Bacillus subtilis vegetative and spore cells was evaluated by determining the time course of the growth heat changes (growth thermogram) with a microbial calorimeter. The actual heat evolution curve (f (t) curve) obtained from the thermogram was in good agreement with the viable cell number changes. From the logarithmic f (t) curve, the exponential growth phase was estimated to be the period of between 31 and 35 h after inoculation and the growth rate constant (mu') was 0.36 h(-1). The f (t) curve was also obtained from the thermogram of the spore cells. The starting time of growth of the spore cells was 9 h later than that of the vegetative cells. This period corresponded to the germination period. The growth profile after germination was almost similar to that of the vegetative cells. The suppressive activities of sucrose monopalmitate (SMP) against the vegetative and spore cells were evaluated by the f (t) curves. Our results show that SMP inhibited metabolic inductions during the lag phase of the vegetative cells and the germination of the spore cells. Microbial calorimetry is a method suitable for non-destructive growth measurements of microbial colonies on the surface of a solid medium.